1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, a printer and a facsimile using a two-component developer including a toners and a carrier, and to an image developer used therein.
2. Discussion of the Background
Typically, in an image forming apparatus using a two-component developer (hereinafter referred to as a “developer”), a toner consumed for development is fed into the developer and the developer is stirred to recover the concentration of the toner of the developer in the image developer and perform constant developability even when time passes. Recently, the image developer includes circulation paths including at least a first path the developer fed onto the surface of a developer bearer passes through and a second path connected with the first path directly or through another path. The image developer stirs the developer in the second path and feed the developer to the first path to be fed onto the surface of a developer bearer. Therefore, the image developer has deviation of toner concentration in the developer due to insufficient stir less than an image developer having none of such circulation paths. However, even the image developer including the circulation paths has a deviation of toner concentration in the developer unless the developer is fully stirred on the second path.
Japanese published unexamined application No. 2004-205535 discloses an image developer including a circulation path, in which a mesh member is fitted between blades of a stirring and feeding screw. When the stirring and feeding screw rotates, the developer is fed in the rotational axial direction of the stirring and feeding screw and passed through the mesh member for plural times. Therefore, the dispersibility of a toner in the developer can be improved and the deviation of the toner concentration therein can be reduced.
Recent image forming apparatuses are becoming smaller, and an image forming engine has smaller capacity, resulting in difficulty of obtaining a space for containing a developer in the image developer. On the other hand, it is necessary to obtain a space for containing a developer in the image developer to a degree. Consequently, in the image developer, each path in a developer container containing the developer is mostly occupied with the developer and does not have sufficient vacant space. When the path in the developer container does not have sufficient vacant space, the developer cannot widely move even when stirred and the developers in separated places are difficult to exchange each other. Therefore, even the image developer disclosed in Japanese published unexamined application No. 2004-205535 cannot obtain a sufficient stirring effect when having insufficient vacant spaces, resulting in difficulty of reducing the deviation of the toner concentration.
Because of these reasons, a need exists for an image forming apparatus capable of obtaining a sufficient stirring effect of the developer even when having insufficient vacant spaces in the paths in the developer container.